[Leetcode] 729. My Calendar I 解题报告

题目：

Implement a MyCalendar class to store your events. A new event can be added if adding the event will not cause a double booking.

Your class will have the method, book(int start, int end). Formally, this represents a booking on the half open interval [start, end), the range of real numbers x such that start <= x < end.

A double booking happens when two events have some non-empty intersection (ie., there is some time that is common to both events.)

For each call to the method MyCalendar.book, return true if the event can be added to the calendar successfully without causing a double booking. Otherwise, return false and do not add the event to the calendar.

Your class will be called like this:  MyCalendar cal = new MyCalendar();   MyCalendar.book(start, end)

Example 1:

MyCalendar();
MyCalendar.book(10, 20); // returns true
MyCalendar.book(15, 25); // returns false
MyCalendar.book(20, 30); // returns true
Explanation: 
The first event can be booked.  The second can't because time 15 is already booked by another event.
The third event can be booked, as the first event takes every time less than 20, but not including 20.

Note:

The number of calls to  MyCalendar.book per test case will be at most  1000. In calls to  MyCalendar.book(start, end),  start and  end are integers in the range  [0, 10^9].

思路：

我们用一个set来表示截止目前的所有时间段。然后当book一个新的segment的时候，找到它应该所处的位置，并分别看它和前后相邻的segments是否有重合。如果有则返回false，否则插入当前的segment，并且返回true。

代码：

class MyCalendar {
public:
    MyCalendar() {
        
    }
    
    bool book(int start, int end) {
        vector p = {start, end};
        auto next = segments.upper_bound(p);
        if (next != segments.end()) {   // check whether has an intersection with the next segment
            if (p[1] > (*next)[0]) {
                return false;
            }
        }
        if (next != segments.begin()) { // check whether has an intersection with the previous segment
            --next;
            if (p[0] < (*next)[1]) {
                return false;
            }
        }
        segments.insert(p);
        return true;
    }
private:
    set> segments;
};

/**
 * Your MyCalendar object will be instantiated and called as such:
 * MyCalendar obj = new MyCalendar();
 * bool param_1 = obj.book(start,end);
 */